Because of their advantages such as low power consumption and low environmental load, light emitting diodes (LEDs) have recently been used in various electrical and electronic products such as small displays of mobile communication devices including mobile phones, etc., medium and large displays of personal computers, liquid crystal TVs, etc., console panels of automobiles and interior lights for automobiles, household lights, signs and indicator lights, traffic lights, and other household appliances.
An LED is usually used as an LED package, and the LED package is mainly composed of a semiconductor element (LED) that emits light, a lead wire, a reflector serving also as a housing, and a transparent sealing material for sealing the semiconductor element. Ceramics are known as materials used for such reflectors. However, the use of ceramics for reflectors causes problems of low productivity and low initial reflectance. Heat-resistant plastics also are known as materials used for reflectors. For example, Patent Literatures 1 to 5 disclose the use of polyamide compositions containing titanium oxide as heat-resistant plastics for the reflectors.
A heat-resistant plastic reflector is required to have heat resistance because it is exposed to temperatures of 100° C. to 200° C. for several hours when a conductive adhesive or a sealing agent is thermally cured during the production of an LED package. The reflector is also required to retain a high light reflectance (in particular, a high reflectance for light with a wavelength of around 460 nm for use in a white LED), without being discolored when it is exposed to high temperatures during the production of an LED package or in the environment in which the reflector is used in the LED package. It is further required to have good mechanical properties as a reflector. It is also required to have high adhesion to the sealing material.
Thus, the heat-resistant plastic reflector is required to have various properties, and the techniques described in Cited Literatures 1 to 5 have room for improvement.